1. Field of the Invention
The present invention relates to a method and apparatus for doubling the frequency of a periodic input signal.
2. Description of Related Art
Integrated circuits often utilize an external clock source such as a crystal oscillator. To reduce the cost of such circuits, it is desirable to use lower frequency crystals, and to multiply the frequency produced by these crystal oscillators on chip.
Known frequency doubling circuits use phased-locked loops, but these are large and complex circuits. A simpler alternative would be to use a circuit that produces pulses off both the rising and falling edges of an incoming clock signal to double the frequency of the incoming clock signal. Unfortunately, however, such a circuit produces pulses with widths that vary greatly based on the applied voltage, circuit fabrication process and operating temperature.